Draft

ADVISORY BOARD ON

RADIATION AND WORKER HEALTH

National Institute for Occupational Safety and Health

SC&A’S EVALUATION OF NIOSH’S WHITE PAPER, 

“REASSESSMENT OF INTERNAL RADIATION DOSE FROM 

SOURCES AT THE ROCKY FLATS PLANT CRITICAL MASS 

LABORATORY,” OF NOVEMBER 28, 2016

Contract No. 211-2014-58081 

SCA-TR-2017-SEC003, Revision 0 

Prepared by

Ron Buchanan, PhD, CHP 

SC&A, Inc.

1608 Spring Hill Road, Suite 400 

Vienna, Virginia, 22182 

Saliant, Inc.

5579 Catholic Church Road 

Jefferson, Maryland 21755 

January 2017 

DISCLAIMER

This is a working document provided by the Centers for Disease Control and Prevention (CDC) technical 

support contractor, SC&A for use in discussions with the National Institute for Occupational Safety and 

Health (NIOSH) and the Advisory Board on Radiation and Worker Health (ABRWH), including its 

Working Groups or Subcommittees. Documents produced by SC&A, such as memorandum, white paper, 

draft or working documents are not final NIOSH or ABRWH products or positions, unless specifically 

marked as such. This document prepared by SC&A represents its preliminary evaluation on technical 

issues.

NOTICE: This report has been reviewed to identify and redact any information that is protected by the 

Privacy Act 5 U.S.C. § 552a and has been cleared for distribution.
Effective Date:

01/24/2017

Revision No.

0 (Draft)

Document No./Description:

SCA-TR-2017-SEC003

Page No.

2 of 9

NOTICE: This report has been reviewed to identify and redact any information that is protected by the 

Privacy Act 5 U.S.C. § 552a and has been cleared for distribution. 

SC&A, INC.: Technical Support for the Advisory Board on Radiation and Worker 

Health Review of NIOSH Dose Reconstruction Program

DOCUMENT TITLE: 

SC&A’s Evaluation of NIOSH’s White Paper, “Reassessment of 

Internal Radiation Dose from Sources at the Rocky Flats Plant Critical 

Mass Laboratory,” of November 28, 2016

DOCUMENT NUMBER/

DESCRIPTION:

SCA-TR-2017-SEC003 

REVISION NO.: 0 (Draft)

SUPERSEDES: N/A

EFFECTIVE DATE: January 24, 2017

TASK MANAGER: Joe Fitzgerald [signature on file]

PROJECT MANAGER: John Stiver, MS, CHP [signature on file]

DOCUMENT 

REVIEWER(S): John Stiver, MS, CHP [signature on file] 

Record of Revisions

Revision 

Number

Effective 

Date Description of Revision

0 (Draft) 01/24/2017 Initial issue
Effective Date:

01/24/2017

Revision No.

0 (Draft)

Document No./Description:

SCA-TR-2017-SEC003

Page No.

3 of 9

NOTICE: This report has been reviewed to identify and redact any information that is protected by the 

Privacy Act 5 U.S.C. § 552a and has been cleared for distribution. 

TABLE OF CONTENTS

Abbreviations and Acronyms ......................................................................................................... 4

1.0 Introduction and Background ............................................................................................. 5

2.0 Outline of NIOSH’s Report ................................................................................................ 5

3.0 SC&A’s Evaluation ............................................................................................................ 8

4.0 Summary and Conclusions ................................................................................................. 8

5.0 References ........................................................................................................................... 9
Effective Date:

01/24/2017

Revision No.

0 (Draft)

Document No./Description:

SCA-TR-2017-SEC003

Page No.

4 of 9

NOTICE: This report has been reviewed to identify and redact any information that is protected by the 

Privacy Act 5 U.S.C. § 552a and has been cleared for distribution. 

ABBREVIATIONS AND ACRONYMS

CML Critical Mass Laboratory

Cs cesium

DOE U.S. Department of Energy 

dpm disintegrations per minute 

f intake fraction

HEU high-enriched uranium

IMBA Integrated Modules for Bioassay Analysis

MFAP mixed fission and activation products 

mrem millirem

μCi microcurie

μCi/g microcuries per gram

mW milliwatt

NIOSH National Institute for Occupational Safety and Health

ORAUT Oak Ridge Associated Universities Team

RFP Rocky Flats Plant

Sr strontium 
Effective Date:

01/24/2017

Revision No.

0 (Draft)

Document No./Description:

SCA-TR-2017-SEC003

Page No.

5 of 9

NOTICE: This report has been reviewed to identify and redact any information that is protected by the 

Privacy Act 5 U.S.C. § 552a and has been cleared for distribution. 

1.0 INTRODUCTION AND BACKGROUND 

In March 2016, representatives from the National Institute for Occupational Safety and Health 

(NIOSH) and SC&A, Inc. evaluated documents stored at the Los Alamos National Laboratory 

from the former Critical Mass Laboratory (CML) located at the Rocky Flat Plant (RFP), Golden, 

Colorado. In November 2016, NIOSH issued Reassessment of Internal Radiation Dose from 

Sources at the Rocky Flats Plant Critical Mass Laboratory: White Paper (NIOSH 2016), which 

evaluated the potential mixed fission and activation products (MFAP) exposure at the RFP CML. 

The following sections contain SC&A’s evaluation of NIOSH’s report. 

2.0 OUTLINE OF NIOSH’S REPORT

To facility the evaluation of NIOSH’s report (NIOSH 2016), SC&A outlines the main sections of 

the report, as follows:

• Purpose (page 2): The purpose of the report was to reevaluate potential MFAP exposures 

at the CML because, according to the report: 

A publicly released document [NIOSH 2015] citing a maximum reactor 

operating power of 10 milliwatts (mW) and typical experiment duration of 

one hour were previously used to estimate the MFAP inventory built up 

over time in high-enriched uranium (HEU) solution fuel used in CML 

experiments.... 

In the earlier assessment, internal doses from the estimated MFAP 

inventory were bounded by assuming removable surface contamination 

from dried solution spills to be at the limit for a posted Contamination 

Area. The average air concentration of respirable particles was then 

estimated by applying a resuspension factor. Recently captured documents 

contain air monitoring results, surface contamination measurements, 

more-accurate power estimates based on carefully measured gamma 

photon emissions from the irradiated fuel, records of experiment duration, 

and neutron flux profiles. This information provides data against which 

the prior assumptions can be re-evaluated. 

• Exposure Concerns (page 2): CML personnel were monitored for alpha-emitting

radionuclides but not routinely for MFAP. Additionally, surfaces and equipment were 

routinely monitored for alpha contamination, but not for MFAP contamination. 

• History of Criticality Experiments (pages 3 and 4): A total of 778 subcritical and 

critical experiments were conducted from May 1967 through October 1987. 

• Thermal Power and Fission Rates (pages 5–8): Several methods of estimating the 

thermal power and fission rates are provided in this section. The experiment that was 

reported to the Energy Research and Development Administration on June 3, 1977 (and 

produced the greatest number of fissions), had an average power of 6.7 mW with an 

experiment time of 70.5 minutes (compared to 10 mW for 1 hour as previously used). 
Effective Date:

01/24/2017

Revision No.

0 (Draft)

Document No./Description:

SCA-TR-2017-SEC003

Page No.

6 of 9

NOTICE: This report has been reviewed to identify and redact any information that is protected by the 

Privacy Act 5 U.S.C. § 552a and has been cleared for distribution. 

• CML Surface Alpha Contamination (pages 8–20): According to pages 8–9 of 

NIOSH’s report (NIOSH 2016): 

Internal doses from the estimated MFAP inventory were bounded in the 

earlier estimate by assuming that removable surface contamination from 

dried solution spills was evenly dispersed over CML surfaces at the DOE 

[U.S. Department of Energy] limit (1,000 dpm [disintegrations per 

minute]/100 cm2) for a posted Contamination Area. The average air 

concentration of respirable particles was then estimated by applying a 

resuspension factor. Recently captured documents contain both air 

monitoring and surface contamination measurement results against which 

the prior assumptions can be reevaluated.

Information on pages 8–20 provides examples of alpha contamination survey results 

during the 1980s at the CML. Note that these results are for alpha activity, not MFAP 

activity (MFAP would consist of mainly beta/gamma emitters). This section is included 

in NIOSH’s report to support the following statements on page 20: 

Surveys for removable alpha contamination at CML were conducted 

regularly. Excursions above the applicable DOE limits (20 dpm/100 cm2

in uncontrolled office areas and 1,000 dpm/100 cm2

 in controlled-access 

experimental areas) were confined to discrete areas and were quickly 

decontaminated below the limits.... 

In light of the above information, the assumption that average removable 

contamination available for resuspension in the experimental and material 

storage areas (Rooms 101, 102, and 103) was equal to or less than the 

Contamination Area limit of 1,000 dpm/100 cm2 is claimant-favorable. 

• CML Workplace Air Alpha Monitoring (pages 20–29): According to page 20 of 

NIOSH’s report:

Bounds on internal dose from MFAP were previously based on airborne 

concentrations calculated by applying a resuspension factor to surface 

contamination limits posted for the facility....

NIOSH has since captured formal plant-wide procedures describing a 

particulate air monitoring program during the period from 1980-1989 for 

alpha-particle emissions from uranium, plutonium, and americium at 

sampling locations selected by process knowledge or professional 

judgment. Additional captured documents indicate that these procedures 

appear to have been followed and that routine alpha air monitoring was 

performed at the CML during the period 1980-1989. 

This section of NIOSH’s report presents air sampling results for alpha activity during the 

1980s at the CML. The purpose of this information is to derive the bounding value of 

alpha activity in air of 13.5 dpm/m3, as show on page 29 of the report. This value was 
Effective Date:

01/24/2017

Revision No.

0 (Draft)

Document No./Description:

SCA-TR-2017-SEC003

Page No.

7 of 9

NOTICE: This report has been reviewed to identify and redact any information that is protected by the 

Privacy Act 5 U.S.C. § 552a and has been cleared for distribution. 

then used on page 35 to derive the radionuclide intake fraction (f) from the fuel mixture 

of 1.5×10-7, which was used later on page 35 of NIOSH’s report to determine the MFAP 

intakes from the fuel mixture.

• Assessment of Unmonitored Dose from MFAP (pages 30–35): NIOSH estimated the 

potential MFAP intake and doses at CML using the following procedure: 

1. MFAP inventory (pages 30–32): NIOSH used a combination of the computer 

programs SCALE, TRITON, and ORIGEN-S to derive a list of MFAP and associated 

activities resulting from a typical critical experiment lasting 70.5 minutes at an 

average power level of 6.7 mW. 

2. Radionuclide selection (pages 33–34): NIOSH used methods from ORAUT-OTIB0054, Revision 03, Fission and Activation Product Assignment for Internal DoseRelated Gross Beta and Gross Gamma Analyses, to select the dosimetricallysignificant radionuclides from the MFAP inventory. These 36 radionuclides and their 

activities (in becquerels) are listed in Table 9, page 34, of NIOSH’s report. 

3. Activity intake fraction (page 35): NIOSH used the following assumptions to 

estimate the potential intake fraction from the fuel mixture:

• The HEU contained 70 microcuries per gram (μCi/g) of alpha activity (SC&A 

verified that this value is consistent with other DOE sites that handled enriched 

uranium). 

• There were 2,783 grams of HEU in the experimental tank (using a tank of 

27.92 cm in diameter and filled to a height of 31.2 cm with a fuel solution of 

density of 145.68 g/L, which is approximately the middle value of 10 RFP 

experiments as described in Palmer 2004, Table 6, page 8. 

• Using these parameters, there was a total of 1.95E3 μCi of alpha activity in the 

fuel (i.e., 70 μCi/g x 2,783 g = 1.95E3 μCi). 

• After the experiment, it was assumed that the relative ratios of the alpha-emitting 

radionuclides were the same in the fuel, surface contamination, and air (i.e., there 

were no situations or processes that selected or concentrated certain 

radionuclides). The same assumption was applied to the MFAP radionuclides. 

• The bounding measured alpha activity was 13.5 dpm/m3. 

• Over a 2-year period (as used in ORAUT-OTIB-0054) the potential intake would 

be 0.0292 μCi of alpha activity (i.e., 13.5 dpm/m3 × 1.2 m3/hr × 2000 hr/y × 2y × 

4.5E-7 μCi/dpm = 0.0292 μCi). 

• The alpha intake fraction (f) would be: 

f = [0.0291 μCi]/[1.95E3 μCi] = 1.5E-7. 
Effective Date:

01/24/2017

Revision No.

0 (Draft)

Document No./Description:

SCA-TR-2017-SEC003

Page No.

8 of 9

NOTICE: This report has been reviewed to identify and redact any information that is protected by the 

Privacy Act 5 U.S.C. § 552a and has been cleared for distribution. 

• This intake fraction would also apply to MFAP present in the fuel. 

4. MFAP intakes (page 35): The MFAP radionuclide activities in Table 9 were 

multiplied by the derived intake fraction value of 1.5E-7 to obtain the potential 

MFAP intakes. 

5. Maximum dose (page 35): The 50-year committed organ doses were derived and 

summed over the 36 MFAP radionuclides listed in Table 9 for solubility Types F, M, 

and S for 25 individual organs. The resulting maximum organ doses for the three 

solubility types are listed in Table 10. The largest dose, 2.5E-9 sievert (2.5E-4 mrem) 

would be to the bone surface from Type F solubility MFAP over a 50-year period.

3.0 SC&A’S EVALUATION

SC&A evaluated NIOSH’s methodology, assumptions, and parameters and verified the 

calculations, some of which are illustrated in Section 2.0 of this report. Additionally, SC&A 

verified some of the important references that NIOSH used in its analyses. SC&A did not rerun 

the computer simulation programs (SCALE, etc.) or the 36 radionuclide doses to 25 organs 

because this would have required considerable additional resources. SC&A did verify that the 

radionuclides and their relative activities listed in Table 9 (NIOSH 2016) were reasonable 

compared to the MFAP listed in Table 7a of ORAUT-OTIB-0054. SC&A also performed 

Integrated Modules for Bioassay Analysis (IMBA) runs for some of the most dose-significant 

radionuclides (with their associated activities from Table 9, modified by the intake fraction of 

1.5E-7) for solubility Types F, M, and S and arrived at total 50-year committed organ doses of 

much less than 0.001 rem, which concurs with NIOSH’s results in Table 10 of the white paper 

(NIOSH 2016). Additionally, SC&A ran the ORAUT-OTIB-0054 workbook program using 

strontium-90 (Sr-90) (and also cesium-137 [Cs-137]) as the indicating radionuclide (with the 

Sr-90 or Cs-137 radionuclide activities as listed in Table 9, modified by the intake fraction of 

1.5E-7) to determine potential MFAP organ doses from typical reactor fuels with 180-day decay 

(as listed in Table 7a of ORAUT-OTIB-0054) and derived 50-year committed organ doses that 

were much less than 0.001 rem, which also concurs with NIOSH’s results. 

4.0 SUMMARY AND CONCLUSIONS

SC&A’s evaluation of NIOSH’s methodology indicates that NIOSH used reasonable and 

claimant-favorable assumptions and parameters in deriving the potential MFAP intakes and 

doses for CML workers at the RFP. SC&A did not identify any outstanding errors in the 

calculations or any data issues in NIOSH’s process. Various parameters and scenarios could be 

used to estimate the potential MFAP intakes at the CML, with differing results. However, as 

indicative of the very small MFAP doses derived by both NIOSH and SC&A, even a change of a 

factor of 10 or 100 in the results would not alter the conclusions that the potential doses from 

MFAP were very small, and much less than 1 mrem, the minimum dose used in dose 

reconstruction. 
Effective Date:

01/24/2017

Revision No.

0 (Draft)

Document No./Description:

SCA-TR-2017-SEC003

Page No.

9 of 9

NOTICE: This report has been reviewed to identify and redact any information that is protected by the 

Privacy Act 5 U.S.C. § 552a and has been cleared for distribution.

5.0 REFERENCES

NIOSH 2015. Assessment of Sealed Radioactive Sources, and Fission and Activation Products 

as Radiological Exposure Sources in the Rocky Flats Plant Critical Mass Laboratory (Building 

886 Cluster): White Paper, Revision 0, National Institute for Occupational Safety and Health, 

Division of Compensation Analysis and Support, Cincinnati, Ohio. June 9, 2015.

NIOSH 2016. Reassessment of Internal Radiation Dose from Sources at the Rocky Flats Plant 

Critical Mass Laboratory: White Paper, Revision 0, National Institute for Occupational Safety 

and Health, Division of Compensation Analysis and Support, Cincinnati, Ohio. November 28, 

2016.

ORAUT-OTIB-0054. 2015. Fission and Activation Product Assignment for Internal DoseRelated Gross Beta and Gross Gamma Analyses, Revision 03, Oak Ridge Associated 

Universities, Cincinnati, Ohio. February 6, 2015.

Palmer 2004, Minimally Reflected Cylinders of Highly Enriched Solutions of Uranyl Nitrate,

NEA/NSC/DOC(95)03/II, Volume II, HEU-SOL-THERM-001, from the International 

Handbook of Evaluated Criticality Safety Benchmark Experiments, Brian Palmer, Idaho 

Chemical Processing Plant. September 30, 2004. [SRDB Ref. ID 142464]